Well, according to help.sap.com: http://help.sap.com/saphelp_nw04/helpdata/en/62/459f34f36311d3a6510000e835363f/content.htm
SSF requires the use of a security product to perform its functions. Per default, we deliver the SAP Security Library (SAPSECULIB) as the security provider. SAPSECULIB is a software solution with capabilities limited to digital signatures. For support of crypto hardware (for example, smart cards or crypto boxes) or digital envelopes, we also offer the SAP Cryptographic Library, which is available for download on the SAP Service Marketplace.